They said Bhandari was in regular touch with Bansal’s nephew Vijay Singla, arrested for allegedly receiving Rs. 90 lakh from senior rail ministry official Mahesh Kumar, part of a Rs. 10-crore deal for a lucrative post on the railway board.

“Bhandari will definitely be questioned,” a CBI official said.

Bhandari, a 1997-batch Punjab cadre IAS officer, could not be reached for comment despite repeated attempts. He has been with Bansal for a while, having served with him earlier in the water resources ministry.

The agency also arrested Ajay Garg after the alleged middleman surrendered in a city court on Tuesday, the ninth arrest in the case. According to CBI sources, Garg is heard promising Kumar the post of his choice in a phone conversation tapped by the agency that clearly reflects he is working on Singla’s behalf. The CBI is in possession of 1,000 such phone transcripts.

"As far as questioning Pawan Kumar Bansal is concerned, his role is being verified at the moment as the bribe accepted by Singla was clearly meant for somebody in the railway ministry" said a source.

According to the CBI, Kumar, member (staff) on the railway board, wanted to become member (electrical) in place of Kulbhushan, who is to be elevated as chairman when Mittal retires in June.

In addition, Kumar wanted additional charge as general manager (western railway) and signal and telecommunication for the two months it would take for him to be made member (electrical).

He struck a deal with Singla, Garg and another of Singla's associates, Sandeep Goyal, for the postings and agreed to pay Rs. 2 crore immediately.

Kumar delivered part of this amount (Rs. 90 lakh) to Singla and Goyal in Chandigarh. He arranged the bribe money from railway contractors NR Manjunath, Rahul Yadav, Samir Sandhir and Sushil Daga, promising them contracts in future.

Singla, Goyal and Garg were sent to CBI custody for further questioning by special CBI judge Swarana Kanta Sharma on Tuesday.

Investigators said Singla, Goyal and Manjunath were proving tough nuts to crack as their replies are evasive and contrary to the tapped conversations.